The present invention relates to an image inputting apparatus such as a scanner or the like which reads image information by scanning a document, and to an image forming apparatus such as a digital copier or the like which uses the image inputting apparatus.
Conventionally, there are generally two types of CCD line sensors which are used in a reduction optical system: a CCD line sensor which is structured by only a one-line line sensor, and a CCD line sensor which is structured by a three-line line sensor in which color filters of red (hereinafter denoted as R), green (hereinafter denoted as G), and blue (hereinafter denoted as B) are disposed on the surfaces of the respective line sensors.
The aforementioned one-line CCD line sensor is basically used for reading monochrome (white/black) documents. When a color document is read by using this CCD line sensor, a method is adopted in which, by successively turning on three light sources having spectral characteristics of R, G, B which are three primary colors of light, the image information of the color document is divided into color information of R, G, B and read. Further, there is a method which uses a light source whose spectrum characteristic is white, and color filters of R, G, B are disposed on the optical path from the light source to the line sensor, and by switching the color filters, the color information which is incident on the line sensor is separated.
The aforementioned three-line CCD line sensor is basically used for reading color documents. For the light source in this case, a light source which has a spectral characteristic which sufficiently covers the visible light region from oscillation wavelengths of 400 nm to 700 nm is used. The division of the color information of R, G, B is carried out by the color filters which are disposed on the surfaces of the respective line sensors.
Further, when a monochrome document is read by using the three-line line sensor, there are cases in which one output among the three line sensors, generally, the line sensor output of G, is used in order to reliably read a vermilion impression, and there is a method in which white/black information is generated by using all of the outputs of the three line sensors.
When color information is read by a CCD sensor which is structured by a one-line sensor, as described above, a method of the switching light sources or switching the color filters is used. Thus, there are disadvantages in that the control of the light source relationships is complicated, and costs accompanying such control increase.
When single color information is read by using one line sensor output of a CCD sensor which is structured by a three-line sensor, for example, in a case in which the line sensor having sensitivity of G is used, as described above, information in vermilion can be read. However, the green color information and the white information on the document cannot be distinguished from one another, and as a result, information of green characters or images or the like cannot be read. In the same way, in a case in which the line sensor having sensitivity of R is used, a drawback arises in that the red information cannot be read, and in a case in which the line sensor having sensitivity of B is used, a drawback arises in that the blue information cannot be read.
In a case in which white/black information is generated by using all of the outputs of the three line sensors, because the three line CCD sensor is arranged such that the three line sensors are disposed to be physically separate from one another, the respective line sensors cannot read the information at the same area. Accordingly, in order to correct the offset of the positions, it is necessary to effect correction in line units by using line buffers.
Further, at the time of reading, if the distances between the lines of the three line sensors are in a proportional relationship which is an integer multiple of a one-line reading range in the subscanning direction on the document, precise alignment can be achieved by the aforementioned line buffers. However, because the one-line reading range in the subscanning direction varies in accordance with the reading magnification, there is the problem that the above-described proportional relationship is not established, and the alignment of color information by the line buffers is poor. Moreover, in a case in which an image is rapidly changed from white to black or from black to white such as a monochrome characters, the drawback that false colors such as red or blue are generated at the changing points arises.